Day 155: Noctilucent Clouds!

Very basically, noctilucent clouds are made up of tiny ice crystals very high in the atmosphere (about 47-53 miles up) and are only visible in summer months at latitudes between 50 and 70 degrees north or south of the equator when the sun lights them up from below the horizon.  In this photo you can see the normal clouds too which is a nice illustration of the difference in looks and how you can tell a noctilucent cloud from a normal one.  They're a pretty exciting thing to see because of the beautiful ethereal glow they give off.  They are also interesting as not much is known about them and there is only a relatively short period of time where they are observable.  For the astronomer frustrated by the light summer skies they are a welcome challenge to spot and observe - as well as being the only clouds we will put up with!